Water-based ink for ink-jet recording and cartridge

ABSTRACT

A water-based ink for ink-jet recording includes a self-dispersible pigment modified by phosphate group; water; a water-soluble organic solvent; at least one of a cationic polymer and basic amino acid; and at least one selected from the group consisting of boric acids, a chelate agent, a reducing sugar and a sugar alcohol.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priorities from No. 2011-188027 filed onAug. 30, 2011, Japanese Patent Application No. 2011-188028 filed on Aug.30, 2011, Japanese Patent Application No. 2011-188029 filed on Aug. 30,2011 and Japanese Patent Application No. 2011-188030 filed on Aug. 30,2011, the disclosures of which are incorporated herein by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a water-based ink for ink-jetrecording, and ink cartridge.

2. Description of the Related Art

In a water-based ink for ink-jet recording, a self-dispersible pigmentis used in some cases. The self-dispersible pigment can be obtained byperforming a treatment such that at least one hydrophilic group such asphosphate group, carboxylic group, or sulfonate group (sulfonic acidgroup), or a salt thereof is bonded to the pigment. Since theself-dispersible pigment does not require any polymeric pigmentdispersant, the self-dispersible pigment is capable of preventing theviscosity of the water-based ink from increasing. Further, aself-dispersible pigment, among the hydrophilic groups each bonded tothe pigment, which is treated in particular with the phosphate group canobtain high optical density (OD value) as compared with aself-dispersible pigment which is treated with the carboxylic group orthe sulfonate group.

On the other hand, the water-based ink using the self-dispersiblepigment treated with the phosphate group has a problem such that the inkcomposition thereof generally does not have satisfactory re-dispersionproperty. In a case that the water-based ink which does not have thesatisfactory re-dispersion property is once evaporated to dryness withresultant solid matter in the vicinity of an ink channel and/or nozzlesof an ink-jet head, the following situation may possibly arise. That is,in a case that the water-based ink is tried to be jetted again and thatthe solid matter is newly brought in contact with the water-based ink,the solid matter is not dissolved and dispersed. Thus, it is feared thatany trouble occurs in jetting stability.

In view of the above situation, an object of the present teaching is toprovide a water-based ink for ink-jet recording which includes aself-dispersible pigment, which has excellent re-dispersion property,and which can obtain relatively-high optical density (OD value).

SUMMARY OF THE INVENTION

According to the first aspect of the present teaching, there is provideda water-based ink for ink-jet recording including: a self-dispersiblepigment modified by phosphate group; water; a water-soluble organicsolvent; at least one of a cationic polymer and basic amino acid; and atleast one selected from the group consisting of boric acids, a chelateagent, a reducing sugar and a sugar alcohol.

According to the second aspect of the present teaching, there isprovided an ink cartridge containing the water-based ink for ink-jetrecording as defined in the first aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing an example of aconstruction of an ink-jet recording apparatus according to the presentteaching.

FIGS. 2A to 2C are diagrams showing evaluation criteria of re-dispersionproperty in examples of the present teaching.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to achieve the object as described above, the inventors foundout, through a series of diligent research and study, excellentre-dispersion property and high optical density (OD value) can beobtained in a case that a self-dispersible pigment modified by phosphategroup is used as a coloring agent and further that at least one of acationic polymer and basic amino acid and at least one selected from thegroup consisting of boric acids, a chelate agent, a reducing sugar, anda sugar alcohol are contained in a water-based ink for ink-jetrecording. Then, the inventors arrived at the present teaching.

In the present teaching, the term “re-dispersion property” means, forexample, solubility and dispersion property of a solid matter, in awater-based ink, generated after the water-based ink is once evaporatedto dryness with resultant solid matter, the solubility and dispersionproperty being those of when the solid matter is then newly brought incontact with the water-based ink.

An explanation will be made about a water-based ink for ink-jetrecording of the present teaching (hereinafter sometimes referred to as“water-based ink” or “ink”). The water-based ink of the present teachingcontains a colorant, water, and a water-soluble organic solvent. Asdescribed above, the colorant includes a self-dispersible pigmentmodified by phosphate group (hereinafter sometimes referred to as“phosphate group-modified self-dispersible pigment). By containing thephosphate group-modified self-dispersible pigment as the colorant, it ispossible to obtain the water-based ink having high optical density (ODvalue). Further, as will be described later on, by containing at leastone of the cationic polymer and the basic amino acid in the water-basedink, it is possible to obtain the water-based ink having even higheroptical density (OD value). The phosphate group-modifiedself-dispersible pigment can be prepared by methods described in, forexample, Published Japanese Translation of PCT International Publicationfor Patent Application Nos. 2009-515007 (PCT International PublicationWO2007/053564), 2011-515535, 2009-513802, 2011-510155 and JapanesePatent Application laid-open No. 2006-199968. It is allowable to use,for example, a commercially available product as the phosphategroup-modified self-dispersible pigment. Since the water-based ink ofthe present teaching uses the self-dispersible pigment, the water-basedink of the present teaching has no problem of viscosity increase due toa polymeric pigment dispersant and has excellent handling property.

The pigment, which is usable as the raw material for theself-dispersible pigment, includes, for example, carbon black, aninorganic pigment, and an organic pigment. The carbon black includes,for example, furnace black, lamp black, acetylene black, channel black,etc. The inorganic pigment includes, for example, titanium oxide,inorganic pigments based on iron oxide, and inorganic pigments based oncarbon black. The organic pigment includes, for example, azo-pigmentssuch as azo lake, insoluble azo-pigment, condensed azo-pigment, chelateazo-pigment and the like; polycyclic pigments such as phthalocyaninepigment, perylene and perynon pigments, anthraquinone pigment,quinacridone pigment, dioxadine pigment, thioindigo pigment,isoindolinone pigment, quinophthalone pigment and the like; dye lakepigments such as basic dye type lake pigment, acid dye type lake pigmentand the like; nitro pigments; nitroso pigments; aniline black daylightfluorescent pigment; and the like. Further, other than the above, thepigments also include, for example, C. I. Pigment Blacks 1, 6, and 7; C.I. Pigment Yellows 1, 2, 3, 12, 13, 14, 15, 16, 17, 55, 78, 150, 151,154, 180, 185, and 194; C. I. Pigment Oranges 31 and 43; C. I. PigmentReds 2, 3, 5, 6, 7, 12, 15, 16, 48, 48:1, 53:1, 57, 57:1, 112, 122, 123,139, 144, 146, 149, 166, 168, 175, 176, 177, 178, 184, 185, 190, 202,221, 222, 224, and 238; C. I. Pigment Violet 196; C. I. Pigment Blues 1,2, 3, 15, 15:1, 15:2, 15:3, 15:4, 16, 22, and 60; C. I. Pigment Greens 7and 36; and the like. In particular, a pigment which is suitable to bemodified with the phosphate group includes, for example, the carbonblack such as “MA8” and “MA100” produced by Mitsubishi ChemicalCorporation and “Color Black FW200” produced by Degussa.

The phosphate group-modified self-dispersible pigment can be prepared bya publicly known method. The method for preparing the phosphategroup-modified self-dispersible pigment is, for example, as follows.Hereinbelow, an explanation will be made about a method for preparationof a carbon black modified by a group having the formula—CO—NH—CH(PO₃H₂)₂ or salts thereof (preparation method 1) and a methodfor preparation of a carbon black modified by a group having the formula—SO₂—NH—CH(PO₃H₂)₂ or salts thereof (preparation method 2).

[Preparation Method 1]

Aminomethylenebisphosphonate (AMBP) is prepared as shown in Scheme 1below using one of the following methods.

<Method A>Phosphorus acid (750 g, 9.15 moles, 1.6 equiv) is charged into a reactorprovided with a mechanical stirrer, a condenser with a guard tube, awater condenser, a thermometer, and an addition funnel under a nitrogenatmosphere. To this is added 1,4-dioxane (1.5 L) followed by formamide(250 g, 5.56 moles, 1 equiv) with stirring. The nitrogen atmosphere isremoved, and the mixture is warmed to 60° C. for 1 hour and then cooledbacked to 20° C. Phosphorus trichloride (1.5 L, 17.19 moles, 3.1 equiv)is added to the mixture over a period of 3 hours, and the resultingmixture is then heated to 60° C. for 3 hours. During the heating, thereaction mixture turns into a white sticky mass, which is difficult tostir towards the end. Heating and stirring is discontinued, and thereaction mixture is allowed to stand at room temperature overnight.After removing the liquid phase by decanting, water (2.5 L) is added tothe reaction mass for the hydrolysis, and this is then heated to refluxfor 4 hours. The reaction mixture is cooled to room temperature,filtered, washed with methanol (2.5 L), and dried under vacuum, yieldingAMBP as a white solid (540 g, 51% yield). ¹HNMR data for this compound(D₂O/NaOH) is as follows: 2.56 (t, 1H, J=16.4 Hz). LC-MS data for thiscompound is as follows: 190 [M-1].<Method B>To a stirred mixture of formamide (500 g, 11.11 mol) and phosphorus acid(800 g, 9.75 mol) in a 20 L multi-neck round bottom flask provided withan overhead mechanical stirrer, a water condenser with a guard tube, athermometer, and a liquid addition funnel is added deionized water (600mL, 33.33 mol). The mixture is cooled to 10° C. in an ice water bath,and to this is added 0.5 L of phosphorus trichloride (note: the additionof phosphorus trichloride to water is exothermic) over a period of 3hours followed by another addition of 0.5 L of phosphorus trichlorideover a period of 30 minutes at a temperature of below 20-25° C. When allof the water is consumed, the temperature drops to below 10° C., and tothis is added 2.5 L of phosphorus trichloride over a period of 15minutes (total phosphorus trichloride addition is 3.5 L, 40 mol). Tocontrol the frothing, the stirrer is lifted up in the flask and stirredat a higher rate. Then the reaction mixture is warmed to 60° C. in 2 to2.5 hours and continued at that temperature until the reaction masssolidifies and can not stir further (approximately 1 hour after reaching60° C.). Heating and stirring is discontinued, and the reaction mixtureis left as is overnight for slow cooling to 40° C. Any remaining excessphosphorus trichloride is decanted off, and 1 L demineralized water isadded to the reaction mixture over a period of 4 hours under a nitrogenatmosphere (heat evolution of this quenching process is controlled byportion-wise addition of water to avoid the presence of excess water,which may react violently). The reaction mixture is stirred forapproximately 0.5 hour, and then another 4 L demineralized water isadded and heated to reflux for 6 hours. The resulting mixture is allowedto cool to 35° C. overnight and is then filtered, washed with 2 Ldeionized water followed by 2 L acetone, and dried at reduced pressureovernight, yielding AMBP as a white solid (830 g, 39% yield). ¹HNMR datafor this compound (400 MHz, D₂O—NaOH) is as follows: 2.56 (t, 1H, J=16.4Hz). LC-MS data for this compound is as follows: 190 [M-I].

AMBP is reacted with 4-nitrobenzoylchloride as shown in Scheme 2 below.

A mixture of p-nitrobenzoic acid (500 g, 3.0 moles, 1 equiv) and thionylchloride (600 mL, 8.2 moles, 2.73 equiv) is heated to reflux forapproximately 6-7 hours until a clear solution is obtained. Excess ofthionyl chloride is removed by distillation followed by co-distillationwith toluene (300 mL). The reaction mass is cooled to room temperature,and hexane (1.5 L) is added, forming a precipitate, which is thenfiltered and dried under vacuum, yielding 4-nitrobenzoyl chloride as ayellow solid (530 g, approximately 100% yield), which is used withoutany further purification.

AMBP (450 g, 2.35 moles, 1 equiv) is suspended in de-ionized water (9L). To this is added a 10N aqueous sodium hydroxide solution to adjustthe pH to 10.0. To this is then added all of the previously prepared4-nitrobenzoyl chloride over a period of 1 hour, while maintaining thereaction pH at 10.1-10.2 by addition of the 10N aqueous sodium hydroxidesolution as needed. After the addition is completed, the reactionmixture is warmed to 60-65° C. in a preheated oil bath. The pH ismaintained at 10.0 by continued addition of the 10N aqueous NaOHsolution until no further drop in pH is observed. After 1.5 hours ofheating, the reaction mixture is cooled to room temperature andfiltered. The pH of the filtrate is adjusted to 3.9 by addition of a 5Naqueous HCl solution, and the resulting precipitate, containing mostlyp-nitrobenzoic acid, is removed by filtration. The filtrate (whichcontains Compound (a) with approximately 9% p-nitrobenzoic acid) is usedwithout further purification.

The filtrate containing Compound (a) is reacted as shown in Scheme 3below.

The pH of the filtrate is adjusted to 8.5 by addition of a 10N aqueousNaOH solution. To this is added 5% Pd/C (50% wet, 16 g, 1 wt % assuming800 g of Compound (a) in the filtrate). The mixture is hydrogenated in aParr shaker at 6 kg/cm² hydrogen pressure at room temperature until nofurther pressure decrease is observed. The pressure is released, and thereaction mixture is filtered through a celite bed. The pH of thefiltrate is adjusted to 1.5 by addition of a 5N aqueous HCl solution.The resulting precipitate is isolated by filtration and washedsuccessively with 1:1 methanol-water, methanol, and finally withacetone. The resulting product is dried at reduced pressure overnight,yielding Compound (b) as a white solid (600 g, 82% yield). ¹HNMR (400MHz) data for this compound (D₂O) is as follows: 7.73 (d, 2H, J=8.4 Hz),6.88 (d, 2H, J=8.4 Hz), 4.29 (t, 1H, J=18.8 Hz). ¹³CNMR (100 MHz) datafor this compound (D₂O) is as follows: 171.1, 153.2, 131.9, 127.2, 118.3and 53.9 (t). LC-MS data for this compound is as follows: 309 [M-I].

The phosphate group-modified self-dispersible pigment is prepared usingone of the following general procedures. The methods, pigment types asspecific raw materials, and specific amounts of Compound (b) (treatmentlevel, mmol of Compound (b) per gram of carbon black) are shown in TABLE1 below.

TABLE 1 No. Method Pigment Treatment Level (mmols/g) 1A A BP1000 0.75 1BA BP700 0.75 1C B BP880 0.25 1D B BP880 0.35 1E B BP880 0.50

In TABLE 1, BP1000 is Black Pearls (trade name) 1000 carbon black (acarbon black having a BET surface area of 343 m²/g and a DBPA of 105mL/100 g), BP700 is Black Pearls (trade name) 700 carbon black (a carbonblack having a BET surface area of 200 m²/g and a DBPA of 117 mL/100 g),and BP880 is Black Pearls (trade name) 880 carbon black (a carbon blackhaving a BET surface area of 220 m²/g and a DBPA of 105 mL/100 g), eachavailable from Cabot Corporation.

<Method A>

20 g of a carbon black, 20 mmol of Compound (b) and 200 mL of DI waterare mixed with a Silverson mixer (6000 rpm) at room temperature. If thepH of the resulting slurry is greater than 4, 20 mmol of nitric acid isalso added. After 30 min, sodium nitrite (20 mmol) in a small amount ofwater is added slowly into the mixture. The temperature reaches 60° C.through mixing, and this is allowed to proceed for 1 hour. The phosphategroup-modified self-dispersible pigment is produced. The pH is adjustedto 10 with a NaOH solution. After 30 min, the resulting dispersion ofthe phosphate group-modified self-dispersible pigment, comprising apigment having attached at least one geminal bisphosphonic acid group orsalts thereof, is diafiltered with a Spectrum membrane using 20 volumesof DI water and concentrated to approximately 12% solids and sonicatedfor 30 min to achieve a desired particle size.<Method B>

A ProcessAll 4HV Mixer (4 liter) is charged with 500 g of dry carbonblack, 1 L of DI water, and Compound (b). The resultant mixture is thenheated to 60° C. while intensely mixing at 300 RPM for 10 minutes. Tothis is added a 20% aqueous sodium nitrite solution (1 molar equivalentbased on the amount of Compound (b)) over 15 minutes. Heating and mixingis continued for a total of 3 hours. The contents of the mixer areremoved by diluting with an additional 750 mL of DI water, and theresulting dispersion of the phosphate group-modified self-dispersiblepigment is then purified by diafiltration using DI water. At the end ofthe diafiltration (permeate conductivity<200 micro Siemens) theconcentration of the phosphate group-modified self-dispersible pigmentin the dispersion is adjusted to 15% and then centrifuged in a CarrContinuous Centrifuge (PilotFuge).

For each dispersion, the sodium content is measured with an Orion IonSelective Electrode, and the results, expressed on a solid basis, areshown in TABLE 2 below. Also, the total amount of phosphorous ismeasured by elemental analysis, and the results, expressed as a weightpercent, are also shown in TABLE 2 below. Also shown are the mean volumeparticle sizes (nm) of the modified pigment in the dispersions, measuredusing a Microtrac (trade mark) Particle Size Analyzer.

TABLE 2 No. Particle Size (nm) Na (ppm) % P 1A 120 27868 2.31 1B 14520658 2.25 1C 106 11608 1.34 1D 102 14621 1.54 1E 104 19940 2.20[Preparation Method 2]Compound (c) is prepared from AMBP using the procedure described inPreparation Method 1, with the exception that 4-nitrobenzenesulfonylchloride is used in place of 4-nitrobenzoyl chloride. The reaction isshown in Scheme 4 below.

Thus, to a suspension of 375 g of AMBP (1.96 mmol) in 3 L deionizedwater is added a 10N NaOH solution (600 ml). The addition is donerapidly in order to dissolve the AMBP at ambient temperature (reactiontemperature is observed to increase to 40° C.). Then, the pH of thereaction mixture is adjusted to 9.9 by using a 10N NaOH solution.4-Nitrobenzenesulfonyl chloride is added to this portion-wise over aperiod of 1.5 hours, maintaining the pH at 9.75-9.9 by adding a 10N NaOHsolution as needed. The reaction temperature is observed to increase to48-50° C. at the end of the addition, and stirring is continued foranother 30 minutes at this temperature until the pH is steady at 9.8.¹HNMR analysis of the mixture shows 52% conversion. The reaction mixtureis filtered hot, cooled to 40° C., and the pH of the filtrate isadjusted to 1.3 by adding 500 ml of concentrated HCl. This is furthercooled to 15-20° C. in an ice water bath and stirred for 1.5-2 hours andleft overnight. The resulting precipitated solid is filtered, washedwith 2 L of methanol followed by 2 L of acetone, and dried under reducedpressure to obtain the desired product having a ¹HNMR purity ofapproximately 55%. To the residual mother liquor is added an equalvolume (5.5 L) of methanol. This is stirred for 1 hour, and theresulting precipitated solid is filtered, washed with 1 L methanolfollowed by 1 L acetone, and dried under reduced pressure to obtainadditional product, which has a ¹HNMR purity of approximately 45%. Thetwo batches of solids are combined, yielding the desirednitrobenzylsulfonamide as a white solid (approximately 700 g having apurity of approximately 50%), which is used as is for the hydrogenationstep. ¹HNMR data for this compound (400 MHz, D₂O—NaOH) is as follows:8.38 (2H, d, 8 Hz), 8.12 (2H, d, 8 Hz), 3.79 (1H, t, 20 Hz) and 2.6 (1H,t, 17.6 Hz).

The sulfonamide product is suspended over deionized water (3 L) andstirred for 5 minutes. Any insoluble starting material is removed byfiltration (70 g). To the filtrate is added 120 mL of a 10N NaOHsolution in order to adjust the pH to 8.5. To this solution is added 5%Pd/C (50% by weight-wet), and the mixture is hydrogenated at 10 kg/sqcmH₂ pressure for 3 hours at room temperature. ¹HNMR analysis of thereaction mixture shows the absence of starting material. The reactionmixture is filtered through celite, and the pH of the filtrate isreadjusted to 0.95 by addition of 200 mL of 10N HCl. The resultingprecipitate is filtered, washed with water (1 L) followed by acetone (1L), and dried under reduced pressure at 60° C., yielding Compound (c) asa white solid (180 g, 88% yield). ¹HNMR data for this compound (400 MHz,D₂O/NaOH) is as follows: 7.73 (2H, d, 8.8 Hz), 6.79 (2H, d, 8.8 Hz),3.45 (1H, t, 18.4 Hz). ¹³CNMR data for this compound (400 MHz, D₂O/NaOH)is as follows: 152.5, 131.1, 130.7, 116.3 and 55.1 (t). LC-MS data forthis compound is as follows: 345 [M-23].

A dispersion of the phosphate group-modified self-dispersible pigment isprepared using Method B, described in Preparation Method 1 above, usingCB-C as the pigment and Compound (c) at a treatment level of 0.35 mmolesof Compound (c) per gram of carbon black. Particle size, sodium content,and total amount of phosphorous for this modified pigment are shown inTABLE 3 below.

TABLE 3 Example Partucle Size (nm) Na (ppm) % P No. 114 12792 1.08

The solid content blending amount (pigment solid content) of thephosphate group-modified self-dispersible pigment with respect to theentire amount of the water-based ink is not particularly limited, andmay be appropriately determined based on, for example, desired opticaldensity or color (hue, tint), etc. The pigment solid content is, forexample, 0.1% by weight to 20% by weight, is preferably 1% by weight to10% by weight, and is more preferably 2% by weight to 8% by weight.

The colorant may further contain any other pigment, dye, etc., inaddition to the phosphate group-modified self-dispersible pigment; or itis allowable that the colorant does not contain any other pigment, dye,etc. That is, it is allowable that the phosphate group-modifiedself-dispersible pigment is singly used as the colorant. Further, it isallowable that a self-dispersible carbon black is singly used as thephosphate group-modified self-dispersible pigment.

The water used in the water-based ink is preferably ion-exchanged wateror pure water (purified water). The blending amount of water (waterratio) with respect to the entire amount of the water-based ink is, forexample, 10% by weight to 90% by weight, and is preferably 40% by weightto 80% by weight. The water ratio may be, for example, the balance ofthe ink, excluding the other components.

The water-soluble organic solvent used in the water-based ink includes,for example, a humectant which prevents the water-based ink from dryingat an end of the nozzle in the ink-jet head and a penetrant whichadjusts the drying speed of the water-based ink on a recording medium.

The humectant is not particularly limited, and includes, for example,lower alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol,isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, and tert-butylalcohol; amides such as dimethylformamide and dimethylacetamide; ketonessuch as acetone; ketoalcohols (ketone alcohols) such as diacetonealcohol; ethers such as tetrahydrofuran and dioxane; polyvalent(polyhydric) alcohols such as polyalkylene glycol, alkylene glycol,glycerol, and trimethylolpropane; 2-pyrrolidone; N-methyl-2-pyrrolidone;and 1,3-dimethyl-2-imidazolidinone. The polyalkylene glycol includes,for example, polyethylene glycol and polypropylene glycol. The alkyleneglycol includes, for example, ethylene glycol, propylene glycol,butylene glycol, diethylene glycol, triethylene glycol, dipropyleneglycol, tripropylene glycol, thiodiglycol, and hexylene glycol. It isallowable that only one kind of the humectant as described above is usedsingly, or two or more kinds of the humectants are used in combination.Among the above-described humectants, it is preferable to use polyvalentalcohols such as alkylene glycol, glycerol, etc.

The blending amount of the humectant with respect to the entire amountof the water-based ink is, for example, 0% by weight to 95% by weight,is preferably 5% by weight to 80% by weight, and is more preferably 5%by weight to 50% by weight.

The penetrant includes, for example, glycol ether. The glycol etherincludes, for example, ethylene glycol methyl ether, ethylene glycolethyl ether, ethylene glycol-n-propyl ether, diethylene glycol methylether, diethylene glycol ethyl ether, diethylene glycol-n-propyl ether,diethylene glycol-n-butyl ether, diethylene glycol-n-hexyl ether,triethylene glycol methyl ether, triethylene glycol ethyl ether,triethylene glycol-n-propyl ether, triethylene glycol-n-butyl ether,propylene glycol methyl ether, propylene glycol ethyl ether, propyleneglycol-n-propyl ether, propylene glycol-n-butyl ether, dipropyleneglycol methyl ether, dipropylene glycol ethyl ether, dipropyleneglycol-n-propyl ether, dipropylene glycol-n-butyl ether, tripropyleneglycol methyl ether, tripropylene glycol ethyl ether, tripropyleneglycol-n-propyl ether, and tripropylene glycol-n-butyl ether. It isallowable that only one kind of the penetrant as described above is usedsingly, or two or more kinds of the penetrants are used in combination.

The blending amount of the penetrant with respect to the entire amountof the water-based ink is, for example, 0% by weight to 20% by weight,is preferably 0.1% by weight to 15% by weight, and is more preferably0.5% by weight to 10% by weight.

As described above, the water-based ink further includes at least one ofthe cationic polymer and the basic amino acid and at least one selectedfrom the group consisting of the boric acids, the chelate agent, thereducing sugar, and the sugar alcohol. It is assumed that it is possibleto obtain the water-based ink having the excellent re-dispersionproperty by containing at least one selected from the group consistingof the boric acids, the chelate agent, the reducing sugar, and the sugaralcohol; and that it is possible to obtain the water-based ink havingthe higher optical density (OD value) than conventional water-based inksby containing at least one of the cationic polymer and the basic aminoacid. The present teaching, however, is not limited to this assumption.

The boric acids include, for example, oxo acid of boron such asorthoboric acid, metaboric acid, tetraboric acid, and a salt thereof(including hydrate). The oxo acid may be generated by hydrating boricoxide. In particular, the boric acids include, for example, ammoniumborate (ammonium tetraborate tetrahydrate, ammonium pentaborateoctahydrate, etc.); potassium borate (potassium tetraborate tetrahydrateetc.); lithium borate (lithium tetraborate (anhydrous), lithiumtetraborate trihydrate, etc.); boric acid; sodium borate (disodiumtetraboric (anhydrous), disodium tetraboric decahydrate, borate soda(borax), etc.); and barium borate. The boric acids are preferably atleast one of ammonium borate and potassium borate. However, thecompounds described above are merely examples of the present teaching,and the number of boron atoms, the number of and kinds of positive ionsin borate salt, the number of water molecules in the hydrate, etc., arenot limited thereto. The blending amount of the boric acids with respectto the entire amount of the water-based ink is, for example, 0.01% byweight to 10% by weight, is preferably 0.05% by weight to 3% by weight,and is more preferably 0.1% by weight to 1% by weight. From a viewpointof re-dispersion property, the blending amount of the boric acids withrespect to the entire amount of the water-based ink is preferably 0.5%by weight to 1% by weight. It is allowable that only one kind of theboric acids as described above is used singly, or two or more kinds ofthe boric acids are used in combination.

The chelate agent is not particularly limited, and it is allowable touse publicly known products or substances. The chelate agent includes,for example, ethylenediamine tetraacetic acid, ethylenediamine diaceticacid, nitrilo triacetic acid, 1,3-propanediamine tetraacetic acid,diethylenetriamine pentaacetic acid, N-hydroxyethyl ethylenediaminetriacetic acid, iminodiacetic acid, uramildiacetic acid,1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid, malonic acid,succinic acid, glutaric acid, maleic acid, and salts thereof (includinghydrates). The chelate agent is preferably at least one selected fromthe group consisting of ethylenediamine tetraacetic acid, a salt ofethylenediamine tetraacetic acid, nitrilo triacetic acid, and a salt ofnitrilo triacetic acid. The blending amount of the chelate agent withrespect to the entire amount of the water-based ink is, for example,0.01% by weight to 10% by weight, is preferably 0.05% by weight to 5% byweight, and is more preferably 0.1% by weight to 3% by weight. From aviewpoint of re-dispersion property, the blending amount of the chelateagent with respect to the entire amount of the water-based ink ispreferably 0.5% by weight to 1% by weight. It is allowable that only onekind of the chelate agent as described above is used singly, or two ormore kinds of the chelate agents are used in combination.

The reducing sugar includes, for example, glucose, mannose, galactose,fructose, arabinose, ribose, xylose, erythrose, glyceraldehyde, lactose,maltose, dihydroxyacetone, erythrulose, xylulose, ribulose, psicose,sorbose, tagatose, sedoheptulose, coriose, threose, lyxose, allose,talose, gulose, altrose, and idose. The reducing sugar is preferably atleast one of glucose and xylose. In a case that both of D and L formsare present in the reducing sugar, any one of them or a mixture of bothforms may be used. Similarly, in a case that both of d form(dextro-rotatory, (+)) and I form (levo-rotatory, (−)) are present inthe reducing sugar, any one of them or a mixture of both forms may beused. The blending amount of the reducing sugar with respect to theentire amount of the water-based ink is, for example, 0.01% by weight to30% by weight, is preferably 0.05% by weight to 20% by weight, and ismore preferably 0.2% by weight to 10% by weight. From a viewpoint ofre-dispersion property, the blending amount of the reducing sugar withrespect to the entire amount of the water-based ink is preferably 5% byweight to 10% by weight. It is allowable that only one kind of thereducing sugar as described above is used singly, or two or more kindsof the reducing sugars are used in combination.

The sugar alcohol includes, for example, sorbitol (another name:glucitol), mannitol, iditol, talitol, dulcitol, allodulcitol (anothername: allitol), xylitol, ribitol (another name: adonitol), arabitol,meso-erythritol, threitol, isomalt, lactitol, maltitol, volemitol, andperseitol. Out of these, the sugar alcohol is preferably sorbitol,mannitol, or xylitol from the viewpoint of solubility and ease ofobtaining. The sugar alcohol is more preferably at least one of sorbitoland mannitol. In a case that both of D and L forms are present in thesugar alcohol, any one of them or a mixture of both forms may be used.The blending amount of the sugar alcohol with respect to the entireamount of the water-based ink is, for example, 0.01% by weight to 20% byweight, is preferably 0.05% by weight to 12% by weight, and is morepreferably 0.2% by weight to 8% by weight. From a viewpoint ofre-dispersion property, the blending amount of the sugar alcohol withrespect to the entire amount of the water-based ink is preferably 5% byweight to 8% by weight. It is allowable that only one kind of the sugaralcohol as described above is used singly, or two or more kinds of thesugar alcohols are used in combination.

The water-based ink may contain at least one of the boric acids and thechelate agent. Further, the water-based ink may contain at least one ofthe reducing sugar and the sugar alcohol. The reason why there-dispersion property of the water-based ink is improved by thereducing sugar or the sugar alcohol is not clear, but it is assumed thatwater retention ability is superior due to the chemical structure inwhich many hydroxyl groups are contained, and thereby making it possibleto retain water in the solid matter even in a state that the water-basedink is evaporated and solidified.

It is allowable that any one of the boric acids, the chelate agent, thereducing sugar, and the sugar alcohol is singly used in the water-basedink; or it is allowable that two or more are selected from the groupconsisting of the boric acids, the chelate agent, the reducing sugar,and the sugar alcohol and are used in combination.

The cationic polymer is preferably at least one of compounds representedby the following general formula (1), the following general formula (2),and the following general formula (3).

In the general formulae (1) and (2), R¹ to R³ each are a hydrogen atomor organic group. The organic group is exemplified, for example, byalkyl group and aryl group. The alkyl group may have a straight chain ora branched chain, which is exemplified by methyl group, ethyl group,n-propyl group, isopropyl group, n-butyl group, isobutyl group,sec-butyl group, tert-butyl group, n-hexyl group, cyclohexyl group,n-octyl group, 2-ethylhexyl group, n-decyl group, n-dodecyl group,octadecyl group, 1,3-butadienyl group, 1,3-pentadienyl group, etc. Thearyl group is exemplified, for example, by phenyl group, naphthyl group,tolyl group, and vinyl phenyl group. The alkyl group and aryl group eachmay have a substituent or substituents. The alkyl group and aryl grouphaving the substituent or substituents are exemplified, for example, byfluoroethyl group, trifluoroethyl group, methoxyethyl group,phenoxyethyl group, hydroxyphenylmethyl group, chlorophenyl group,dichlorophenyl group, trichlorophenyl group, bromophenyl group,iodophenyl group, fluorophenyl group, hydroxyphenyl group, methoxyphenylgroup, acetoxyphenyl group, and cyanophenyl group.

In the general formula (2), X⁻ is an anion. The anion may be any; and isexemplified, for example, by a halide ion, a sulfonic acid ion, an alkylsulfonic acid ion, an aryl sulfonic acid ion, an alkylcarbboxylic ion,and an arylcarbboxylic ion.

In the general formulae (1) and (2), “n” is a positive integer, forexample, is 2 to 400, is preferably 5 to 300, and is more preferably 10to 200. Weight-average molecular weight of the compound represented byeach of the general formulae (1) and (2) is not particularly limited,for example, is 200 to 20000, is preferably 500 to 15000, and morepreferably 1000 to 9000.

In the general formula (1), R¹ and R² each are especially preferably ahydrogen atom. In this case, the compound represented by the generalformula (1) is polyallylamine. Further, in the general formula (2), R¹to R³ each are preferably a hydrogen atom, and X⁻ is preferably achloride ion. In this case, the compound represented by the generalformula (2) is polyallylamine hydrochloride (allylamine hydrochloridepolymer).

In the general formula (3), p is an integer of 2 to 6 and q is aninteger of 20 to 40.

In the general formula (3), it is particularly preferably that p is 4.In such a case, the compound represented by the general formula (3) ispolylysine. Further, in the general formula (3), it is preferable that qis 25 to 35.

The compound represented by the general formula (3) may include aderivative of the compound represented by the general formula (3). In acase that an isomer, such as a tautomer or steroisomer (for example,geometric isomer, conformational isomer, and steroisomer), exists in thecompound represented by the general formula (3) and the derivativethereof, it is allowable to use any one of the isomers in the presentteaching. Further, a salt of the compound represented by the generalformula (3) and a salt of the derivative of the compound represented bythe general formula (3) may also be used in the present teaching. Thesalt may be an acid addition salt or a base addition salt. Further, theacid composing the acid addition salt may be an inorganic acid ororganic acid, and the base composing the base addition salt may be aninorganic base or organic base. Although the inorganic acid is notparticularly limited, the inorganic acid is exemplified by hydrochloricacid, sulfuric acid, phosphoric acid, hydrofluoric acid, hydrobromicacid, hydroiodic acid, hypofluorous acid, hypochlorous acid, hypobromousacid, hypoiodous acid, fluorous acid, chlorous acid, bromous acid,iodous acid, fluoric acid, chloric acid, bromic acid, iodic acid,perfluorinated acid, perchloric acid, perbromic acid, periodic acid,etc. Although the organic acid is also not particularly limited, theorganic acid is exemplified by glutamic acid, p-toluenesulfonic acid,methanesulfonic acid, oxalic acid, p-bromobenzenesulfonic acid, carbonicacid, succinic acid, citric acid, benzoic acid, acetic acid, hydroxycarboxylic acid, propionic acid, malonic acid, adipic acid, fumaricacid, maleic acid, etc. Although the inorganic base is not particularlylimited, the inorganic base is exemplified by ammonium hydroxide, alkalimetal hydroxide, alkaline earth metal hydroxide, carbonate,hydrogencarbonate, sulfate, etc.; and the inorganic base is morespecifically exemplified by sodium hydroxide, potassium hydroxide,potassium carbonate, sodium carbonate, sodium hydrogencarbonate,potassium hydrogencarbonate, calcium hydroxide, calcium carbonate,potassium sulfate, calcium sulfate, etc. The organic base is also notparticularly limited, and is exemplified by alcoholamine, trialkylamine,tetraalkylammonium, tris(hydroxymethyl)aminomethane, etc. Thealcoholamine is exemplified by ethanolamine, etc. The trialkylamine isexemplified by trimethylamine, triethylamine, tripropylamine,tributylamine, trioctylamine, etc. The tetraalkylammonium is exemplifiedby tetramethylammonium, tetraethylammonium, tetrapropylammonium,tetrabutylammonium, tetraoctylammonium, etc.

As the cationic polymer, it is allowable to use those other than thecompounds represented by the general formula (1), the general formula(2), and the general formula (3); or it is allowable not to use thoseother than the compounds represented by the general formula (1), thegeneral formula (2), and the general formula (3). It is allowable thatany one of the compounds represented by the general formula (1), thegeneral formula (2), and the general formula (3) is used singly, or twoor more compounds of the compounds represented by the general formula(1), the general formula (2), and the general formula (3) are used incombination. Further, as the cationic polymer, it is allowable thatpolyallylamine which is the compound represented by the general formula(1), polyallylamine hydrochloride which is the compound represented bythe general formula (2), or polylysine which is the compound representedby the general formula (3) is used singly; or two or more compounds ofpolyallylamine, polyallylamine hydrochloride, and polylysine are used incombination. In the water-based ink of the present teaching, from aviewpoint of jetting stability, it is preferable to use polyallylamine,polyallylamine hydrochloride or polylysine.

The cationic polymer other than the compounds represented by the generalformula (1), the general formula (2), and the general formula (3) isexemplified, for example, by polyamine, polyethyleneimine,polyvinylamine, polyvinylpyridine, polyethyleneimine-epichlorohydrinreaction product, polyamide-polyamine resin, polyamide-epichlorohydrinresin, cationic starch, polyvinyl alcohol, polyvinylpyrrolidone,polyamidine, cationic epoxy resin, polyacrylamide, polyacrylic acidester, polymethacrylic acid ester, polyvinyl formamide, aminoacetalizedpolyvinyl alcohol, polyvinyl benzyl onium, dicyandiamide-formalinpolycondensate, dicyandiamide-diethylenetriamine polycondensate,epichlorohydrin-dimethylamine addition polymer, dimethyldiallylammoniumchloride-SO₂ copolymer, dimethyldiallylammonium chloride polymer, andderivatives thereof. Further, the cationic polymer other than thecompounds represented by the general formula (1), the general formula(2), and the general formula (3) is also exemplified, for example, by apolymer of single monomer or a copolymer of a plurality of monomerscomposed of at least one of water-soluble monomers including, forexample, dimethylaminoethyl methacrylate (DM), methacryloxyethyltrimethyl ammonium chloride (DMC), methacryloxyethyl benzyl dimethylammonium chloride (DMBC), dimethylaminoethyl acrylate (DA),acryloyloxyethyl trimethyl ammonium chloride (DMQ), acryloyloxyethylbenzyl dimethyl ammonium chloride (DABC), dimethylaminopropyl acrylamide(DMAPAA), and acrylamide propyl trimethyl ammonium chloride (DMAPAAQ).

It is allowable to prepare the cationic polymer in-house or to use acommercially available product of the cationic polymer. The commerciallyavailable product is exemplified, for example, by “PAA (trade name)-01”,“PAA (trade name)-03”, “PAA (trade name)-08”, and “PAA (trade name)-15”produced by Nitto Boseki Co., Ltd.

The basic amino acid is exemplified, for example, by a compoundrepresented by the following general formula (4). Specific examples ofthe basic amino acid include arginine, ornithine, lysine, histidine,hydroxylysine, tryptophan, desmosine, creatine, γ-aminobutyric acid,etc., among which arginine, ornithine, lysine, histidine are preferable.From a viewpoint of improvement in optical density, arginine and lysineare more preferable.

In the general formula (4), R⁴ is basic functional group havingfunctional group which includes nitrogen atom at the terminal thereof.

As the basic amino acid, it is allowable that any one of arginine,ornithine, lysine, and histidine is singly used; or two or morecompounds are selected from the group consisting of arginine, ornithine,lysine, and histidine and are used in combination.

The basic amino acid may include a derivative of the basic amino acid.In a case that the isomer, such as the tautomer or stereoisomer (forexample, geometric isomer, conformational isomer, and stereoisomer),exists in the basic amino acid and the derivative thereof, it isallowable to use any of the isomers in the present teaching. Further, asalt of the basic amino acid and a salt of the derivative of the basicamino acid may also be used in the present teaching. The salt isexemplified by an acid addition salt. The acid composing the acidaddition salt may be an inorganic acid or organic acid. Although theinorganic acid is not particularly limited, the inorganic acid isexemplified by hydrochloric acid, sulfuric acid, phosphoric acid,hydrofluoric acid, hydrobromic acid, hydroiodic acid, hypofluorous acid,hypochlorous acid, hypobromous acid, hypoiodous acid, fluorine acid,chlorous acid, bromous acid, iodous acid, fluoric acid, chloric acid,bromic acid, iodic acid, perfluorinated acid, perchloric acid, perbromicacid, periodic acid, etc. Although the organic acid is also notparticularly limited, the organic acid is exemplified by glutamic acid,p-toluenesulfonic acid, methanesulfonic acid, oxalic acid,p-bromobenzenesulfonic acid, carbonic acid, succinic acid, citric acid,benzoic acid, acetic acid, hydroxy carboxylic acid, propionic acid,malonic acid, adipic acid, fumaric acid, maleic acid, etc.

Further, at least one of the cationic polymer and the basic amino acidmay be a compound represented by the general formula (3) in which p is 4and q is 1 or more. A compound represented by the general formula (3) inwhich p is 4 and q is 1 is lysine which is the basic amino acid. Acompound in which p is 4 and q is 2 or more is polylysine which is thecationic polymer. That is, both of lysine and polylysine are representedby the general formula (3) and have a common chemical structure in whichp is 4. In the water-based ink of the present teaching, from a viewpointof jetting stability, it is preferable to contain at least one of lysineand polylysine.

The cationic polymer and the basic amino acid produce cation. Thepigment, which is negatively charged by the phosphate group on therecording medium to which the water-based ink is jetted, is consideredto be aggregated by the cation produced from the cationic polymer or thebasic amino acid. Further, it is assumed that the optical density (ODvalue) is improved by the aggregation of the pigment. The opticaldensity of the water-based ink is especially improved by the cationicpolymer or the basic amino acid in a case that the phosphategroup-modified self-dispersible pigment is used as the colorant. Thereason thereof is not clear, but it is assumed that the phosphategroup-modified self-dispersible pigment is more likely to be aggregatedby the cationic polymer or the basic amino acid as compared with thecarboxylic group-modified self-dispersible pigment or the sulfonategroup-modified self-dispersible pigment. Then, the inventors of thepresent teaching have succeeded in improving the re-dispersion propertyof the water-based ink while maintaining the high optical density (highOD value) in the water-based ink containing the phosphate group-modifiedself-dispersible pigment and at least one of the cationic polymer andthe basic amino acid by containing at least one selected from the groupconsisting of the boric acids, the chelate agent, the reducing sugar,and the sugar alcohol in the water-based ink.

In a case that the water-based ink contains the boric acids or thechelate agent, the blending amount of at least one of the cationicpolymer and the basic amino acid with respect to the entire amount ofthe water-based ink is preferably 0.001% by weight to 0.05% by weight,is more preferably 0.003% by weight to 0.04% by weight, and is furthermore preferably 0.005% by weight to 0.03% by weight. In the case, theblending amount of at least one of the cationic polymer and the basicamino acid with respect to the entire amount of the water-based ink maybe 0.001% by weight to 0.03% by weight. Further, in a case that thewater-based ink contains the reducing sugar or the sugar alcohol, theblending amount of at least one of the cationic polymer and the basicamino acid with respect to the entire amount of the water-based ink ispreferably 0.001% by weight to 0.07% by weight, is more preferably0.005% by weight to 0.05% by weight, and is further more preferably0.01% by weight to 0.03% by weight. In the case, the blending amount ofat least one of the cationic polymer and the basic amino acid withrespect to the entire amount of the water-based ink may be 0.005% byweight to 0.03% by weight. By adjusting balance of the water-based inkcomposition so that the contents of both of at least one of the cationicpolymer and the basic amino acid and at least one selected from thegroup consisting of the boric acids, the chelate agent, the reducingsugar, and the sugar alcohol are within the respective optimum ranges asdescribed above, it is possible to further improve the optical value (ODvalue) and the re-dispersion property of the water-based ink at the sametime. It is allowable that one kind of at least one of the cationicpolymer and the basic amino acid is used singly; or two or more kinds ofat least one of the cationic polymer and the basic amino acid are usedin combination.

Further, it is preferable that at least one selected from the groupconsisting of the boric acids, the chelate agent, the reducing sugar,and the sugar alcohol is contained in the water-based ink in a specificweight ratio with respect to the cationic polymer or the basic aminoacid. In a case that the water-based ink contains the boric acids, theweight ratio of the boric acids with respect to the cationic polymer orthe basic amino acid, that is, (boric acids)/(cationic polymer or basicamino acid) is preferably 16 to 100. In a case that the water-based inkcontains the chelate agent, the weight ratio of the chelate agent withrespect to the cationic polymer or the basic amino acid, that is,(chelate agent)/(cationic polymer or basic amino acid) is preferably 16to 100. In a case that the water-based ink contains the reducing sugar,the weight ratio of the reducing sugar with respect to the cationicpolymer or the basic amino acid, that is, (reducing sugar)/(cationicpolymer or basic amino acid) is preferably 40 to 670. In a case that thewater-based ink contains the sugar alcohol, the weight ratio of thesugar alcohol with respect to the cationic polymer or the basic aminoacid, that is, (sugar alcohol)/(cationic polymer or basic amino acid) ispreferably 40 to 540.

The water-based ink may further contain a conventionally known additive,if necessary. The additive is exemplified, for example, by surfactant,pH-adjusting agent, viscosity-adjusting agent, surface tension-adjustingagent, and fungicide. The viscosity-adjusting agent is exemplified, forexample, by polyvinyl alcohol, cellulose, and water-soluble resin.

The water-based ink can be prepared, for example, as follows. That is,the colorant, water, the water-soluble organic solvent, the boric acids,at least one of the cationic polymer and the basic amino acid, andoptionally other additive component(s) as necessary are mixed uniformlyor homogenously by a conventionally known method. Then, undissolvedmatter(s) is (are) removed by a filter or the like.

Next, an ink cartridge of the present teaching will be explained. Theink cartridge of the present teaching is an ink cartridge which includesa water-based ink for ink-jet recording, wherein the water-based ink isthe water-based ink for ink-jet recording of the present teaching. It isallowable to use, for example, a conventionally known body for inkcartridge as the body of the ink cartridge of the present teaching.

Next, an explanation will be given about an ink-jet recording apparatusand an ink-jet recording method using the same, of the present teaching.The recording includes printing text (character, letter), printing imageor picture, printing, etc.

The ink-jet recording apparatus of the present teaching is an ink-jetrecording apparatus which includes an ink accommodating section and anink discharge mechanism; and which jets ink accommodated in the inkaccommodating section by the ink discharge mechanism, wherein thewater-based ink for ink-jet recording of the present teaching isaccommodated in the ink accommodating section.

FIG. 1 shows a construction of an example of the ink-jet recordingapparatus of the present teaching. As shown in FIG. 1, an ink-jetrecording apparatus 1 includes four ink cartridges 2, an ink dischargemechanism (ink-jet head) 3, a head unit 4, a carriage 5, a driving unit6, a platen roller 7, and a purge device 8 as main constitutivecomponents or parts.

The four ink cartridges 2 contain four colors of water-based inksrespectively, the four colors being yellow, magenta, cyan, and black.For example, the water-based black ink is the water-based ink forink-jet recording of the present teaching. It is allowable to usegeneral or commercially available water-based inks as the remaining inksother than the water-based black ink. The ink-jet head 3 disposed on thehead unit 4 performs recording on a recording medium (for example,recording paper sheet) P. The four ink cartridges 2 and the head unit 4are provided or arranged on the carriage 5. The driving unit 6reciprocates the carriage 5 in a linear direction. As the driving unit6, it is possible to use, for example, a conventionally known drivingunit (see, for example, Japanese Patent Application Laid-open No.2008-246821). The platen roller 7 extends in the reciprocating directionof the carriage 5 and is arranged to face or be opposite to the ink-jethead 3.

The purge device 8 sucks or draws unsatisfactory ink (poor ink) whichcontains air bubbles, etc. accumulated or trapped in the ink-jet head 3.As the purge device 8, it is possible to use, for example, aconventionally known purge device (for example, see Japanese PatentApplication laid-open No. 2008-246821).

A wiper member 20 is provided on the purge device 8, at a position onthe side of the platen roller 7 such that the wiper member 20 isadjacent to the purge device 8. The wiper member 20 is formed to have aspatula shape, and wipes a nozzle-formed surface of the ink-jet head 3accompanying with the movement (reciprocating movement) of the carriage5. In FIG. 1, a cap 18 is provided to cover a plurality of nozzles ofthe ink-jet head 3 which is returned to a reset position upon completionof the recording, so as to prevent the water-based ink from drying.

In the ink-jet recording apparatus 1 of the present teaching, the fourink cartridges 2 are provided, together with the head unit 4, on onecarriage 5. However, the present teaching is not limited to this. In theink-jet recording apparatus, each of the four ink cartridges 2 may beprovided on a carriage which is different (separate) from the carriageon which the head unit 4 is provided. Alternatively, each of the fourink cartridges 2 may be arranged and fixed inside the ink-jet recordingapparatus, rather than being provided on the carriage 5. In suchaspects, for example, each of the four ink cartridges 2 and the headunit 4 which is provided on the carriage 5 are connected with a tube,etc., and the water-based ink is supplied from each of the four inkcartridges 2 to the head unit 4 via the tube.

Ink jet recording using the ink-jet recording apparatus 1 is performed,for example, in the following manner. Namely, at first, the recordingpaper sheet P is supplied or fed from a paper feeding cassette or sheetfeeding cassette (not shown) arranged at a side of or at a positionbelow the ink-jet recording apparatus 1. The recording paper sheet P isintroduced or guided between the ink-jet head 3 and the platen roller 7.Then, a predetermined recording is performed on the fed or introducedrecording paper sheet P with the water-based ink discharged or jettedfrom the ink-jet head 3. The water-based ink of the present teaching canbe discharged stably from the ink-jet head 3 because of the excellentre-dispersion property. Further, it is possible to obtain a recordedmatter having the high optical density (OD value) by using thewater-based ink of the present teaching. The recording paper sheet P forwhich the recording has been performed is discharged from the ink-jetrecording apparatus 1. In FIG. 1, a paper feeding mechanism and a paperdischarge mechanism for the recording paper sheet P are omitted.

In the apparatus shown in FIG. 1, an ink-jet head of serial type (serialtype ink-jet head) is adopted. However, the present teaching is notlimited to this. The ink-jet recording apparatus may be an apparatusadopting an ink-jet head of line type (line type ink-jet head).

According to the present teaching, there is provided an ink-jetrecording method for performing recording by discharging the water-basedink from the ink discharge mechanism, wherein the water-based ink forink-jet recording of the present teaching is used as the water-basedink. The ink-jet recording method of the present teaching can bepracticed, for example, by using the ink-jet recording apparatus of thepresent teaching.

EXAMPLES

Next, examples of the present teaching will be explained together withcomparative examples. Note that the present teaching is not limited andis not restricted to the examples and the comparative examples whichwill be described below.

Examples 1-9 and Comparative Examples 1-6

As shown in TABLE 4, each of the water-based inks of Examples 1-9contains the phosphate group-modified self-dispersible carbon black, theboric acids, and at least one of the cationic polymer and the basicamino acid. Components except for the self-dispersible carbon black,which were included in Composition of Water-based Ink (TABLE 4) asindicated below, were mixed uniformly or homogeneously; and thus an inksolvent was obtained. Subsequently, the ink solvent was added to theself-dispersible carbon black dispersed in water, followed by beingmixed uniformly. After that, the obtained mixture was filtrated througha cellulose acetate membrane filter (pore size 3.00 μm) produced by ToyoRoshi Kaisha, Ltd., and thus water-based inks for ink-jet recording inExamples 1-9 and Comparative Examples 1-6 were obtained. The phosphategroup-modified self-dispersible carbon black can be obtained, forexample, by the general manufacturing method as described above.

The water-based inks of Examples 1-9 and Comparative Examples 1-6 weresubjected to (a) re-dispersion property evaluation and (b) opticaldensity (OD value) evaluation with the following method.

(a) Re-dispersion Property Evaluation

The water-based inks of Examples 1-9 and Comparative Examples 1-6 weredripped each in an amount of 12 μL onto glass slides, respectively.Subsequently, the glass slides were stored for duration of one day underan environment of temperature: 100° C., and thus the water-based inkswere evaporated and dried. Several drops (3 drops) of water were drippedby a dripping pipette onto each of solid matters obtained after thewater-based inks were evaporated and dried. The evaluation samplesprepared in such a manner were observed with the naked eye (unaided eye)and by using a ×50-magnification optical microscope. The re-dispersionproperty was visually evaluated in accordance with the followingevaluation criterion.<Evaluation Criterion for Re-dispersion Property>A: As shown in FIG. 2A, the solid matter was completely dissolved anddispersed in the water when being observed both with the naked eye andthe optical microscope.B+: When being observed with the naked eye, the solid matter wascompletely dissolved and dispersed in the water; but when being observedwith the optical microscope, a part of the solid matter remained withoutbeing dissolved and dispersed in the water.B: Although the solid matter was gradually dissolved and dispersed inthe water, a part of the solid matter remained without being dissolvedand dispersed in the water when being observed with the naked eye. Whenbeing observed with the optical microscope, the solid matter was in astate as shown in FIG. 2B.B−: The solid matter was dissolved and dispersed to an extent that thecolor of the water was slightly changed to the color of the solidmatter; but a part of the solid matter remained as a clod.C: As shown in FIG. 2C, the solid matter was not dissolved and dispersedin the water at all and remained as the clod when being observed bothwith the naked eye and the optical microscope.(b) Optical Density (OD Value) EvaluationA digital multifunction machine DCP-385C provided with an ink-jetprinter produced by Brother Industries, Ltd. was used to record an imageincluding a single-color black patch with the water-based inks ofExamples and Comparative Examples, at a resolution of 600 dpi×600 dpi,on a regular paper sheet, and evaluation samples were prepared. Theoptical density (OD value) of each of the evaluation samples wasmeasured by using a spectrophotometric colorimetry meter SpectroEye(light source: D₅₀; density: ANSI T; reference white: Abs; built-in(internal) filter: NO) produced by X-Rite. Three types of regular papersheets were used as the regular paper sheet. “Hammermill Laser Print(trade name)” produced by International Paper Company was used as aregular paper sheet 1. “Business” produced by XEROX CORPORATION was usedas a regular paper sheet 2. “Recycled Supreme” produced by XEROXCORPORATION was used as a regular paper sheet 3. The measurement of theoptical density (OD value) was performed such that the measurement wasperformed five times for one regular paper sheet.

The compositions and evaluation results of the water-based inks ofExamples 1-9 and Comparative Examples 1-6 are shown in TABLE 4. Notedthat in TABLE 4, “an average of the three types of regular paper sheets”described in the last line (column) for each of the Examples andComparative Examples is an average value of the measurement results ofthe three types of regular paper sheets obtained as follows. That is,the respective average values (five measurements) of the three types ofregular paper sheets were summed up; the summed value was divided bythree.

TABLE 4 EXAMPLES EX. 1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7 EX. 8Water-based ink composition (wt %) Phosphate group-modified self- 4.04.0 4.0 4.0 4.0 4.0 4.0 4.0 dispersible carbon black (*1) Potassiumtetraborate tetrahydrate 1.00 0.10 1.00 0.10 — — — — Ammoniumtetraborate tetrahydrate — — — — 0.50 0.10 0.50 0.50 Polyallylamine (*2)0.015 0.001 — — — — — — Polylysine (*3) — — 0.015 0.001 — — — — Arginine— — — — 0.015 0.001 — 0.030 Lysine — — — — — — 0.015 — Glycerol (85%) —— — — — — — — Trimethylolpropane — — — — — — — — Diethylene glycol 10.0010.00 10.00 10.00 10.00 10.00 10.00 10.00 2-pyrrolidone 5.00 5.00 5.005.00 5.00 5.00 5.00 5.00 Acetylenol (trade name) E40 (*4) 0.15 0.15 0.150.15 0.15 0.15 0.15 0.15 Acetylenol (trade name) E100 (*5) — — — — — — —— Water balance balance balance balance balance balance balance balanceBlending amount of cationic 0.015 0.001 0.015 0.001 0.015 0.001 0.0150.030 polymer/basic amino acid (wt %) Evaluation Re-dispersion propertyA B A B B+ B B+ B+ Optical density (OD value) 1.43 1.40 1.43 1.39 1.401.38 1.40 1.41 Average of three type paper sheets EXAMPLES COMPARATIVEEXAMPLES EX. 9 COM. 1 COM. 2 COM. 3 COM. 4 COM. 5 COM. 6 Water-based inkcomposition (wt %) Phosphate group-modified self-dispersible 4.0 4.0 4.04.0 4.0 4.0 4.0 carbon black (*1) Potassium tetraborate tetrahydrate — —— — — — — Ammonium tetraborate tetrahydrate 0.50 — — — — 0.20 0.10Polyallylamine (*2) — 0.015 — — — — — Polylysine (*3) — 0.015 — — — —Arginine 0.005 — — 0.015 — — — Lysine — — — — 0.015 — — Glycerol (85%) —— — — — 11.76 11.76 Trimethylolpropane — — — — — 5.00 5.00 Diethyleneglycol 10.00 10.00 10.00 10.00 10.00 — — 2-pyrrolidone 5.00 5.00 5.005.00 5.00 — — Acetylenol (trade name) E40 (*4) 0.15 0.15 0.15 0.15 0.15— — Acetylenol (trade name) E100 (*5) — — — — — 0.30 0.30 Water balancebalance balance balance balance balance balance Blending amount ofcationic polymer/basic 0.005 0.015 0.015 0.015 0.015 — — amino acid (wt%) Evaluation Re-dispersion property A C C C C B+ B+ Optical density (ODvalue) 1.40 1.42 1.42 1.39 1.39 1.34 1.30 Average of three type papersheets (*1) Prepared by the method described in PCT InternationalPublication No. WO2007/053564 (*2) Non-neutralized product ofpolyallylamine (weight-average molecular weight: 3,000; produced byNitto Boseki Co., Ltd.; active ingredient amount = 20% by weight(parenthesized numerals indicate active ingredient amounts) (*3)Polylysine (weight-average molecular weight: 4000) (*4) POE (4)acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd. (*5) POE(10) acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd.

As shown in TABLE 4, in each of the water-based inks of Examples 1-9,the re-dispersion property was superior and the average optical density(OD value) of the three types of regular paper sheets was high (not lessthan 1.35). In each of the water-based inks of the Examples 1, 3, 5, and7-9 in which the blending amount of at least one of the cationic polymerand the basic amino acid with respect to the entire amount of thewater-based ink was 0.005% by weight to 0.03% by weight, there-dispersion property of the water-based ink was especially excellent.

On the other hand, the re-dispersion property was inferior in each ofthe water-based inks of Comparative Examples 1-4 in which the boricacids were not used.

Further, the average optical density (OD value) of the three types ofregular paper sheets was low (less than 1.35) in each of the water-basedinks of Comparative Examples 5 and 6 in which neither the cationicpolymer nor the basic amino acid was used.

Examples 10-18 and Comparative Examples 7 and 8

As shown in TABLE 5, each of the water-based inks of Examples 10-18contains the phosphate group-modified self-dispersible carbon black, thechelate agent, and at least one of the cationic polymer and the basicamino acid. The water-based inks for ink-jet recording in Examples 10-18and Comparative Examples 7 and 8 were obtained in the same method as theExamples 1-9 as described above based on Composition of Water-based Ink(TABLE 5) as indicated below. Then, the water-based inks of Examples10-18 and Comparative Examples 7 and 8 were subjected to (a)re-dispersion property evaluation and (b) optical density (OD value)evaluation with the same method as the Examples 1-9 as described above.The compositions and evaluation results of the water-based inks ofExamples 10-18 and Comparative Examples 7 and 8 are shown in TABLE 5.For the purpose of reference, compositions and evaluation results of thewater-based inks of Comparative Examples 1-4 are also shown in TABLE 5.

TABLE 5 EXAMPLES EX. 10 EX. 11 EX. 12 EX. 13 EX. 14 EX. 15 EX. 16 EX. 17Water-based ink composition (wt %) Phosphate group-modifiedself-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 carbon black (*1)Nitrilotriacetic acid trisodium salt 1.00 0.10 1.00 0.10 — — — —monohydrate Disodium ethylenediamine tetraacetate — — — — 0.50 0.10 0.500.50 Polyallylamine (*2) 0.015 0.001 — — — — — 0.030 Polylysine (*3) — —0.015 0.001 — — — — Arginine — — — — 0.015 0.001 — — Lysine — — — — — —0.015 — Glycerol (85%) — — — — — — — — Trimethylolpropane — — — — — — —— Diethylene glycol 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.002-pyrrolidone 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Acetylenol (tradename) E40 (*4) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Acetylenol (tradename) E100 (*5) — — — — — — — — Water balance balance balance balancebalance balance balance balance Blending amount of cationicpolymer/basic 0.015 0.001 0.015 0.001 0.015 0.001 0.015 0.030 amino acid(wt %) Evaluation Re-dispersion property A B A B B+ B B+ B+ Opticaldensity (OD value) 1.43 1.38 1.43 1.37 1.40 1.36 1.40 1.44 Average ofthree type paper sheets EXAMPLES COMPARATIVE EXAMPLES EX. 18 COM. 1 COM.2 COM. 3 COM. 4 COM. 7 COM. 8 Water-based ink composition (wt %)Phosphate group-modified self-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0carbon black (*1) Nitrilotriacetic acid trisodium salt — — — — — — —monohydrate Disodium ethylenediamine tetraacetate 0.50 — — — — 0.20 0.10Polyallylamine (*2) 0.005 0.015 — — — — — Polylysine (*3) — — 0.015 — —— — Arginine — — — 0.015 — — — Lysine — — — — 0.015 — — Glycerol (85%) —— — — — 11.76 11.76 Trimethylolpropane — — — — — 5.00 5.00 Diethyleneglycol 10.00 10.00 10.00 10.00 10.00 — — 2-pyrrolidone 5.00 5.00 5.005.00 5.00 — — Acetylenol (trade name) E40 (*4) 0.15 0.15 0.15 0.15 0.15— — Acetylenol (trade name) E100 (*5) — — — — — 0.30 0.30 Water balancebalance balance balance balance balance balance Blending amount ofcationic polymer/basic 0.005 0.015 0.015 0.015 0.015 — — amino acid (wt%) Evaluation Re-dispersion property A C C C C A A Optical density (ODvalue) 1.40 1.42 1.42 1.39 1.39 1.32 1.31 Average of three type papersheets (*1) Prepared by the method described in PCT InternationalPublication No. WO2007/053564 (*2) Non-neutralized product ofpolyallylamine (weight-average molecular weight: 3,000; produced byNitto Boseki Co., Ltd.; active ingredient amount = 20% by weight(parenthesized numerals indicate active ingredient amounts) (*3)Polylysine (weight-average molecular weight: 4000) (*4) POE (4)acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd. (*5) POE(10) acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd.

As shown in TABLE 5, in each of the water-based inks of Examples 10-18,the re-dispersion property was superior and the average optical density(OD value) of the three types of regular paper sheets was high (not lessthan 1.35). In each of the water-based inks of the Examples 10, 12, 14,and 16-18 in which the blending amount of at least one of the cationicpolymer and the basic amino acid with respect to the entire amount ofthe water-based ink was 0.005% by weight to 0.03% by weight, there-dispersion property of the water-based ink was especially excellent.

On the other hand, the re-dispersion property was inferior in each ofthe water-based inks of Comparative Examples 1-4 in which the chelateagent was not used.

Further, the average optical density (OD value) of the three types ofregular paper sheets was low (less than 1.35) in the each of thewater-based inks of Comparative Examples 7 and 8 in which neither thecationic polymer nor the basic amino acid was used.

Examples 19-27 and Comparative Examples 9 and 10

As shown in TABLE 6, each of the water-based inks of Examples 19-27contains the phosphate group-modified self-dispersible carbon black, thereducing sugar, and at least one of the cationic polymer and the basicamino acid. The water-based inks for ink-jet recording in Examples 19-27and Comparative Examples 9 and 10 were obtained in the same method asthe Examples 1-9 as described above based on Composition of Water-basedInk (TABLE 6) as indicated below. Then, the water-based inks of Examples19-27 and Comparative Examples 9 and 10 were subjected to (a)re-dispersion property evaluation and (b) optical density (OD value)evaluation with the same method as the Examples 1-9 as described above.The compositions and evaluation results of the water-based inks ofExamples 19-27 and Comparative Examples 9 and 10 are shown in TABLE 6.For the purpose of reference, compositions and evaluation results of thewater-based inks of Comparative Examples 1-4 are also shown in TABLE 6.

TABLE 6 EXAMPLES EX. 19 EX. 20 EX. 21 EX. 22 EX. 23 EX. 24 EX. 25 EX. 26Water-based ink composition (wt %) Phosphate group-modifiedself-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 carbon black (*1)D(+)-xylose 10.00 0.20 10.00 0.20 — — 10.00 — D(+)-glucose — — — — 5.000.20 — 5.00 Polyallylamine (*2) 0.015 0.005 — — — — — — Polylysine (*3)— — 0.015 0.005 — — — — Arginine — — — — 0.015 0.005 — 0.030 Lysine — —— — — — 0.015 — Glycerol (85%) — — — — — — — 11.76 Trimethylolpropane —— — — — — — 5.00 Diethylene glycol 10.00 10.00 10.00 10.00 10.00 10.0010.00 — 2-pyrrolidone 5.00 5.00 5.00 5.00 5.00 5.00 5.00 — Acetylenol(trade name) E40 (*4) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 — Acetylenol(trade name) E100 (*5) — — — — — — — 0.30 Water balance balance balancebalance balance balance balance balance Blending amount of cationicpolymer/basic 0.015 0.005 0.015 0.005 0.015 0.005 0.015 0.030 amino acid(wt %) Evaluation Re-dispersion property A B A B B+ B A B+ Opticaldensity (OD value) 1.43 1.36 1.43 1.36 1.40 1.35 1.40 1.42 Average ofthree type paper sheets EXAMPLES COMPARATIVE EXAMPLES EX. 27 COM. 1 COM.2 COM. 3 COM. 4 COM. 9 COM. 10 Water-based ink composition (wt %)Phosphate group-modified self-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0carbon black (*1) D(+)-xylose — — — — — — — D(+)-glucose 5.00 — — — —5.00 0.20 Polyallylamine (*2) — 0.015 — — — — — Polylysine (*3) — —0.015 — — — — Arginine 0.010 — — 0.015 — — — Lysine — — — — 0.015 — —Glycerol (85%) 11.76 — — — — 11.76 11.76 Trimethylolpropane 5.00 — — — —5.00 5.00 Diethylene glycol — 10.00 10.00 10.00 10.00 — — 2-pyrrolidone— 5.00 5.00 5.00 5.00 — — Acetylenol (trade name) E40 (*4) — 0.15 0.150.15 0.15 — — Acetylenol (trade name) E100 (*5) 0.30 — — — — 0.30 0.30Water balance balance balance balance balance balance balance Blendingamount of cationic polymer/basic 0.010 0.015 0.015 0.015 0.015 — — aminoacid (wt %) Evaluation Re-dispersion property A C C C C A B Opticaldensity (OD value) 1.40 1.42 1.42 1.39 1.39 1.22 1.26 Average of threetype paper sheets (*1) Prepared by the method described in PCTInternational Publication No. WO2007/053564 (*2) Non-neutralized productof polyallylamine (weight-average molecular weight: 3,000; produced byNitto Boseki Co., Ltd.; active ingredient amount = 20% by weight(parenthesized numerals indicate active ingredient amounts) (*3)Polylysine (weight-average molecular weight: 4000) (*4) POE (4)acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd. (*5) POE(10) acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd.

As shown in TABLE 6, in each of the water-based inks of Examples 19-27,the re-dispersion property was superior and the average optical density(OD value) of the three types of regular paper sheets was high (not lessthan 1.35). In each of the water-based inks of the Examples 19, 21, 23,and 25-27 in which the blending amount of at least one of the cationicpolymer and the basic amino acid with respect to the entire amount ofthe water-based ink was 0.01% by weight to 0.03% by weight, there-dispersion property of the water-based ink was especially excellent.

On the other hand, the re-dispersion property was inferior in each ofthe water-based inks of Comparative Examples 1-4 in which the reducingsugar was not used.

Further, the average optical density (OD value) of the three types ofregular paper sheets was low (less than 1.35) in each of the water-basedinks of Comparative Examples 9 and 10 in which neither the cationicpolymer nor the basic amino acid was used.

Examples 28-36 and Comparative Examples 11 and 12

As shown in TABLE 7, each of the water-based inks of Examples 28-36contains the phosphate group-modified self-dispersible carbon black, thesugar alcohol, and at least one of the cationic polymer and the basicamino acid. The water-based inks for ink-jet recording in Examples 28-36and Comparative Examples 11 and 12 were obtained in the same method asthe Examples 1-9 as described above based on Composition of Water-basedInk (TABLE 7) as indicated below. Then, the water-based inks of Examples28-36 and Comparative Examples 11 and 12 were subjected to (a)re-dispersion property evaluation and (b) optical density (OD value)evaluation with the same method as the Examples 1-9 as described above.The compositions and evaluation results of the water-based inks ofExamples 28-36 and Comparative Examples 11 and 12 are shown in TABLE 7.For the purpose of reference, compositions and evaluation results of thewater-based inks of Comparative Examples 1-4 are also shown in TABLE 7.

TABLE 7 EXAMPLES EX. 28 EX. 29 EX. 30 EX. 31 EX. 32 EX. 33 EX. 34 EX. 35Water-based ink composition (wt %) Phosphate group-modifiedself-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 carbon black (*1)D-mannitol 8.00 0.20 8.00 0.20 — — — — D-sorbitol — — — — 5.00 0.20 5.005.00 Polyallylamine (*2) 0.015 0.005 — — — — — — Polylysine (*3) — —0.015 0.005 — — — — Arginine — — — — 0.015 0.005 — 0.030 Lysine — — — —— — 0.015 — Glycerol (85%) — — — — — — — — Trimethylolpropane — — — — —— — — Diethylene glycol 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.002-pyrrolidone 5.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 Acetylenol (tradename) E40 (*4) 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Acetylenol (tradename) E100 (*5) — — — — — — — — Water balance balance balance balancebalance balance balance balance Blending amount of cationicpolymer/basic 0.015 0.005 0.015 0.005 0.015 0.005 0.015 0.030 amino acid(wt %) Evaluation Re-dispersion property A B A B B+ B B+ B+ Opticaldensity (OD value) 1.42 1.36 1.42 1.35 1.41 1.35 1.41 1.42 Average ofthree type paper sheets EXAMPLES COMPARATIVE EXAMPLES EX. 36 COM. 1 COM.2 COM. 3 COM. 4 COM. 11 COM. 12 Water-based ink composition (wt %)Phosphate group-modified self-dispersible 4.0 4.0 4.0 4.0 4.0 4.0 4.0carbon black (*1) D-mannitol — — — — — — — D-sorbitol 5.00 — — — — 5.000.20 Polyallylamine (*2) — 0.015 — — — — — Polylysine (*3) — — 0.015 — —— — Arginine 0.010 — — 0.015 — — — Lysine — — — — 0.015 — — Glycerol(85%) — — — — — 11.76 11.76 Trimethylolpropane — — — — — 5.00 5.00Diethylene glycol 10.00 10.00 10.00 10.00 10.00 — — 2-pyrrolidone 5.005.00 5.00 5.00 5.00 — — Acetylenol (trade name) E40 (*4) 0.15 0.15 0.150.15 0.15 — — Acetylenol (trade name) E100 (*5) — — — — — 0.30 0.30Water balance balance balance balance balance balance balance Blendingamount of cationic polymer/basic 0.010 0.015 0.015 0.015 0.015 — — aminoacid (wt %) Evaluation Re-dispersion property B+ C C C C A B Opticaldensity (OD value) 1.40 1.42 1.42 1.39 1.39 1.22 1.26 Average of threetype paper sheets (*1) Prepared by the method described in PCTInternational Publication No. WO2007/053564 (*2) Non-neutralized productof polyallylamine (weight-average molecular weight: 3,000; produced byNitto Boseki Co., Ltd.; active ingredient amount = 20% by weight(parenthesized numerals indicate active ingredient amounts) (*3)Polylysine (weight-average molecular weight: 4000) (*4) POE (4)acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd. (*5) POE(10) acethylene glycol, produced by Kawaken Fine Chemicals Co., Ltd.

As shown in TABLE 7, in each of the water-based inks of Examples 28-36,the re-dispersion property was superior and the average optical density(OD value) of the three types of regular paper sheets was high (not lessthan 1.35). In each of the water-based inks of the Examples 28, 30, 32,and 34-36 in which the blending amount of at least one of the cationicpolymer and the basic amino acid with respect to the entire amount ofthe water-based ink was 0.01% by weight to 0.03% by weight, there-dispersion property of the water-based ink was especially excellent.

On the other hand, the re-dispersion property was inferior in each ofthe water-based inks of Comparative Examples 1-4 in which the sugaralcohol was not used.

Further, the average optical density (OD value) of the three types ofregular paper sheets was low (less than 1.35) in each of the water-basedinks of Comparative Examples 11 and 12 in which neither the cationicpolymer nor the basic amino acid was used.

As described above, the water-based ink of the present teaching has theexcellent re-dispersion property and the high optical density (ODvalue). The usage of the water-based ink of the present teaching is notspecifically limited, and the water-based ink of the present teaching iswidely applicable to a variety of kinds of ink-jet recording.

What is claimed is:
 1. A water-based ink for ink-jet recordingcomprising: a self-dispersible pigment modified by phosphate group;water; a water-soluble organic solvent; an additive selected from thegroup consisting of boric acids, a chelate agent, a reducing sugar, asugar alcohol, and combinations thereof; and a cationic polymercontained in an amount ranging from 0.005% by weight to 0.03% by weightbased on a total weight of the water-based ink, wherein the cationicpolymer is selected from the group consisting of general formula (1),general formula (3), and combinations thereof; wherein general formula(1) is given by:

where R¹ and R² are independently a hydrogen atom or organic group, andn is a positive integer; and wherein general formula (3) is given by:

where p is an integer of 2 to 6 and q is an integer of 20 to
 40. 2. Thewater-based ink for ink-jet recording according to claim 1, wherein thecationic polymer is of the general formula (1), and R¹ is a hydrogenatom and R² is a hydrogen atom.
 3. The water-based ink for ink-jetrecording according to claim 1, wherein the cationic polymer is of thegeneral formula (3) and p is
 4. 4. The water-based ink for ink-jetrecording according to claim 1, wherein the cationic polymer is of thegeneral formula (3) and q is an integer from 25 to
 35. 5. Thewater-based ink for ink-jet recording according to claim 1, wherein thecationic polymer is contained in an amount ranging from 0.01% by weightto 0.03% by weight based on the total weight of the water-based ink. 6.The water-based ink for ink-jet recording according to claim 1, whereinthe water-based ink does not contain a dye.
 7. The water-based ink forink-jet recording according to claim 1, wherein the cationic polymer isof general formula (1) and has a weight-average molecular weight rangingfrom 200 to 20000.